1. Field of the Invention
The present invention relates to an apparatus and method for dropping a controlled amount of liquid crystal, and more particularly, to an apparatus and method for dropping a controlled amount of liquid crystal such that an exact and optimal amount of liquid crystal is dispensed onto a substrate for a liquid crystal unit panel.
2. Description of the Related Art
Recently, various portable electric devices such as mobile phones, personal digital assistants (PDA), and notebook computers have been developed, and therefore, the needs for a flat panel display device used in small, light weight, and power-efficient devices for such portable devices have correspondingly increased. To meet such needs, flat panel display device technologies such as liquid crystal display (LCD) technology, plasma display panel (PDP) technology, field emission display (FED) technology, and vacuum fluorescent display (VFD) technology have been actively researched. Of these flat panel display devices, the LCD is highlighted due to current mass production, efficient driving schemes, and superior image quality.
The LCD is a device for displaying information on a screen using refractive anisotropy of liquid crystal. As shown in FIG. 1, the LCD 1 comprises a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed between the lower substrate 5 and the upper substrate 3. The lower substrate 5 is a driving device array substrate. A plurality of pixels (not shown) are formed on the lower substrate 5, and a driving device such as a thin film transistor (TFT) is formed on each pixel. The upper substrate 3 is a color filter substrate, and a color filter layer for reproducing real color is formed thereon. Further, a pixel electrode and a common electrode are formed on the lower substrate 5 and the upper substrate 3, respectively. An alignment layer is formed on the lower substrate 5 and the upper substrate 3 to align liquid crystal molecules of the liquid crystal layer 7 uniformly.
The lower substrate 5 and the upper substrate 3 are attached by a sealing material 9, and the liquid crystal layer 7 is formed therebetween. In addition, the liquid crystal molecules are reoriented by the driving device formed on the lower substrate 5 to control the amount of light transmitted through the liquid crystal layer, thereby displaying information.
Fabrication processes for a LCD device can be divided into a driving device array substrate process for forming the driving device on the lower substrate 5, a color filter substrate process for forming the color filter on the upper substrate 3, and a cell process. These processes will be described with reference to FIG. 2 as follows.
At first, a plurality of gate lines and data lines are arranged on the lower substrate to define a pixel area by the driving device array process and the thin film transistor connected to the both gate line and the data line is formed on the each pixel area (S101). Also, a pixel electrode, which is connected to the thin film transistor to drive the liquid crystal layer according to a signal applied through the thin film transistor, is formed by the driving device array process.
At the same time, R (Red), G (Green), and B (Blue) color filter layers for reproducing the color and a common electrode are formed on the upper substrate 3 by the color filter process (S104).
In addition, the alignment layer is formed on the lower substrate 5 and the upper substrate 3, respectively. Then, the alignment layer is rubbed to induce a surface anchoring (that is, a pretilt angle and alignment direction) to the liquid crystal molecules of the liquid crystal layer between the lower substrate 5 and the upper substrate 3 (S102 and S105). Thereafter, a spacer for maintaining the cell gap constant and uniform is dispersed on the lower substrate 5. Then, the sealing material is applied on an outer portion of the upper substrate 3 to attach the lower substrate 5 to the upper substrate 3 by compression (S103, S106, and S107).
The lower substrate 5 and the upper substrate 3 are made from a glass substrate of larger area. That is, the large glass substrate includes a plurality of unit panel areas in which the driving device such as TFT and the color filter layer are formed on. To fabricate the individual liquid crystal unit panel, the assembled glass substrate should be cut into unit panels (S108). Thereafter, the liquid crystal is injected into the empty individual liquid crystal unit panel through a liquid crystal injection opening (S109). The liquid crystal unit panel filled with the liquid crystal is completed by sealing the liquid crystal injection opening, and each liquid crystal unit panel is inspected (S110).
As described above, liquid crystal is injected through the liquid crystal injection opening. At that time, the injection of the liquid crystal is induced by pressure difference. FIG. 3 shows a device for injecting the liquid crystal into the liquid crystal panel. As shown in FIG. 3, a container 12 in which the liquid crystal is contained is placed in a vacuum chamber 10, and the liquid crystal panel is located on an upper portion of the container 12. The vacuum chamber 10 is connected to a vacuum pump to maintain a vacuum state. Further, a liquid crystal panel moving device (not shown) is installed in the vacuum chamber 10 to move the liquid crystal panel from the upper part of the container 12 to the surface of the liquid crystal to contact an injection opening 16 of the liquid crystal panel 1 with the liquid crystal 14 (this step is called a liquid crystal dipping injection step).
When the vacuum in the chamber 10 is released by introducing nitrogen gas (N2) into the vacuum chamber 10 so that the injection opening of the liquid crystal panel 1 contacts the liquid crystal, liquid crystal 14 is injected into the panel through the injection opening by the pressure difference between the pressure in the liquid crystal panel and the pressure of the vacuum chamber. After the liquid crystal is entirely filled into the panel 1, the injection opening 16 is sealed by a sealing material to seal the liquid crystal layer (this step is called a liquid crystal vacuum injection step).
However, there are several problems in the liquid crystal dipping injection/vacuum injection method as follows.
First, the time needed to inject the liquid crystal into the panel 1 is increased. Generally, a gap thickness between the driving device array substrate and the color filter substrate in the liquid crystal panel is very narrow as order of magnitude of micrometers, and therefore, a very small amount of liquid crystal is injected into the liquid crystal panel per unit time. For example, it takes about 8 hours to inject the liquid crystal completely in fabrication process of the 15 inches-liquid crystal panel 15. Thus, the liquid crystal fabrication process time is increased due to the liquid crystal injection of long time, thereby reducing fabricating efficiency.
Second, the liquid crystal consumption is increased in the above liquid crystal injection method. A small amount of liquid crystal of the liquid crystal contained in the container 12 is injected into the liquid crystal panel 1. However, when the liquid crystal is exposed to atmosphere or to a certain gas, the liquid crystal is contaminated by reaction with the gas. Therefore, the remaining liquid crystal should be discarded after the injection when the liquid crystal 14 contained in the container 12 is injected into a plurality of liquid crystal panels 1, thereby increasing the liquid crystal panel fabrication cost.
Accordingly, the present invention is directed to an apparatus for dispensing liquid crystal and a method for controlling a liquid crystal dropping amount that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus for dropping liquid crystal that dispenses liquid crystal directly onto a glass substrate of larger area corresponding to at least one liquid crystal unit panel area.
Another object of the present invention is to provide an apparatus for dropping liquid crystal and a method for controlling a liquid crystal dropping amount such that a precisely con trolled amount of liquid crystal is automatically dropped.
Still another object of the present invention is to provide an apparatus and a method for compensating an amount of the liquid crystal dropped such that an exact and optimal amount of liquid crystal can be dropped onto a substrate of at least one liquid crystal unit panel area.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a liquid crystal dispensing apparatus for dropping liquid crystal onto a substrate corresponding to at least one unit panel area comprises a liquid crystal dispensing unit to dispense liquid crystal, the liquid crystal dispensing unit including a nozzle having a discharging hole through which the liquid crystal is dropped onto the substrate, a needle moveable between a down position in which the needle blocks the discharging hole and an up position in which the needle is separated from the discharging hole, a spring member to bias the needle toward the down position, and a solenoid coil to provide a magnetic force to move the needle to the up position; an electric power supply unit to provide electric power to the solenoid coil to move the needle to the up position; a gas supply unit to provide a gas pressure to the liquid crystal dispensing unit to drive the liquid crystal through the discharging hole when the needle is in the up position; and a control unit to calculate a dropping amount of the liquid crystal to be dropped on the substrate and to control the electric power supply unit and the gas supply unit such that the calculated dropping amount of the liquid crystal is dispensed onto the substrate.
In another aspect, a method of dispensing a liquid crystal onto a substrate having at least one liquid crystal unit panel area from a liquid crystal dispenser using a gas pressure to dispense liquid crystal therefrom, the liquid crystal dispenser including a nozzle having a discharging opening from which the liquid crystal is dropped, a needle moveable between a down position to block the discharging opening and an up position to open the discharging opening, a spring to bias the needle toward the down position, and a solenoid coil to provide a magnetic force to open the discharging hole comprises the steps of inputting data; calculating a total dropping amount of the liquid crystal to be dropped onto the substrate according to the input data; calculating a dropping position at which liquid crystal is to be dropped onto the substrate according to the calculated total dropping amount; calculating a single dropping amount of the liquid crystal according to the total dropping amount; calculating an amount of electric power to be supplied to the solenoid coil and a gas pressure to be applied onto the liquid crystal in the liquid crystal dispenser according to the calculated single dropping amount; and applying the calculated amount of the electric power to the solenoid coil and supplying the calculated gas pressure to the liquid crystal dispenser.
In another aspect, a liquid crystal dispensing apparatus for dropping liquid crystal onto a substrate comprises a liquid crystal dispensing unit to dispense liquid crystal; a measuring system to measure an amount of liquid crystal dispensed from the dispensing unit; and a controller to receive the measured amount of liquid crystal from the measuring system, the controller comparing the measured amount of liquid crystal with a target amount of liquid crystal to be dispensed and electrically adjusting at least one dispensing characteristic of the liquid crystal dispensing unit if the measured amount is different than the target amount.
In another aspect, a liquid crystal dispensing apparatus for dropping liquid crystal onto a substrate corresponding to at least one unit panel area comprises a liquid crystal dispensing unit to dispense liquid crystal such that the liquid crystal dispensing unit includes a nozzle having a discharging hole through which the liquid crystal is dropped onto the substrate, a needle moveable between a down position in which the needle blocks the discharging hole and an up position in which the needle is separated from the discharging hole, a spring member to bias the needle toward the down position, and a solenoid coil to provide a magnetic force to move the needle to the up position; a dropping amount measuring unit to measure a dropping amount of liquid crystal dropped; a compensating amount calculation unit to compare the measured dropping amount with a target dropping amount to calculate a compensating value; and a compensating control unit to control at least one of the electric power applied to the solenoid coil and the gas pressure according to the compensating value.
In another aspect, a method of dispensing liquid crystal onto a substrate corresponding to at least one unit panel area comprises the steps of filling a liquid crystal dispensing unit with liquid crystal; dispensing a first quantity of liquid crystal onto the substrate; conducting an automated compensation of at least one dispensing characteristic of the liquid crystal dispensing unit; and dispensing a second quantity of the liquid crystal onto the substrate, the second quantity being determined according to the automated compensation.
In another aspect, a method of dispensing a liquid crystal from a liquid crystal dispenser using a gas pressure to dispense liquid crystal therefrom, the liquid crystal dispenser including a nozzle having a discharging opening from which the liquid crystal is dropped, a needle moveable between a down position to block the discharging opening and an up position to open the discharging opening, a spring to bias the needle toward the down position, and a solenoid coil to provide a magnetic force to open the discharging hole comprises the steps of setting a dropping amount of the liquid crystal to be dropped; measuring an amount of liquid crystal dropped; calculating a compensating amount by comparing the set dropping amount with the measured dropping amount; and controlling at least one of an electric power applied to the solenoid coil and the gas pressure applied to the liquid crystal according to the calculated compensating amount.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed.